JP2000200432A - Optical disk reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform quick and accurate focus jumping in an optical disk reproducing device for reproducing a multilayer optical disk. SOLUTION: A TN liquid crystal 305 is inserted into a collimator lens 143, no voltages are applied to the TN liquid crystal 305 when a laser beam is focused on a first recording layer 101, a specified voltage is applied to the TN liquid crystal 305 when a laser beam is focused on a second recording layer 102, and thus the focal distance of the collimator lens 143 is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk reproducing apparatus, and more particularly, to an optical disk reproducing apparatus for reproducing a multilayer optical disk having a plurality of recording layers.

[0002]

2. Description of the Related Art The recording capacity of a general compact disk (CD) currently provided is 640 Mbytes, but recently a digital video disk (DVD) having a recording capacity of 4.7 Gbytes with the increase in density has been developed. ) Is also provided. Further, a two-layer DVD having a recording capacity of 8.5 Gbytes by forming the signal recording surface into two layers has also been proposed (for example, Toshiki Kishi, et al., "Single-side reading dual-layer optical disk", National Technical Report Vol. .4
1, No. 6, 10-16, December 1995).

In order to reproduce a two-layer optical disk having two recording layers (signal recording surfaces), a method of reproducing two signal recording surfaces from one surface of the disk and a method of reproducing one signal recording surface from both surfaces of the disk are described. There is a way to do it.
However, the method of reproducing one signal recording surface from both surfaces is complicated since it is necessary to turn the disk over when reproducing the other signal recording surface after the reproduction of one signal recording surface is completed. It is. Further, it is not possible to immediately reproduce another signal recording surface while reproducing one signal recording surface. For this reason, a method of reproducing two signal recording surfaces from one surface has become mainstream.

A single-sided reading dual-layer optical disk as described above has a reflective recording layer made of aluminum or the like and having a reflectance of 70% or more, and a 30% made of gold or the like as a material.
And a translucent recording layer having a degree of reflectance. An ultraviolet curable resin having a thickness of about 40 μm is interposed between the two recording layers as an intermediate layer.

As described above, in the two-layer optical disk, one of the recording layers is of a semi-transparent type. Therefore, by irradiating a laser beam from one side direction to focus on each recording layer,
Information recorded on the recording layer can be read through an optical pickup device.

In the case of a two-layer optical disc, the objective lens is moved in the optical axis direction in order to refocus the laser beam on the other recording layer during reproduction of one recording layer and to start reproduction of the other recording layer. A so-called focus jump of moving is performed (for example, see Japanese Unexamined Patent Application Publication No.
No. 31).

[0007]

However, the conventional focus jump is performed by a mechanical method of moving the objective lens in the optical axis direction by an actuator for controlling the focusing servo. It takes a long time to move the focal point of the laser beam to the recording layer, and the conventional device is liable to break down.

Further, the distance between the two layers in a two-layer optical disk is not actually uniform over the entire disk, but varies in the radial direction. Therefore, there is a problem that it is difficult to accurately perform a focus jump at any position in a two-layer optical disc.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical disk reproducing apparatus capable of performing a quick focus jump.

It is another object of the present invention to provide an optical disk reproducing apparatus capable of performing an accurate focus jump at any position in a multilayer optical disk.

[0011]

According to a first aspect of the present invention, there is provided an optical disk reproducing apparatus for reproducing a multi-layer optical disk having a plurality of recording layers, and for guiding a laser and a laser beam from the laser to the multi-layer optical disk. And a changing means for changing the focal length of the lens according to the recording layer to be reproduced among the plurality of recording layers.

According to a second aspect of the present invention, in addition to the configuration of the first aspect, the lens is a collimator lens.

According to a third aspect of the present invention, in addition to the configuration of the second aspect, the collimator lens includes a first lens piece and a second lens piece provided to face the first lens piece. The lens includes a lens piece and a transparent member sandwiched between the first and second lens pieces. The changing means changes the refractive index of the transparent member according to the recording layer to be reproduced among the plurality of recording layers.

According to a fourth aspect of the present invention, in addition to the configuration of the third aspect, the transparent member includes a first transparent electrode and a second transparent electrode provided to face the first transparent electrode.
And a liquid crystal sandwiched between the first and second transparent electrodes. The changing means includes a liquid crystal drive circuit for applying a predetermined voltage between the first and second transparent electrodes according to a recording layer to be reproduced among the plurality of recording layers.

According to a fifth aspect of the present invention, in addition to the configuration of the fourth aspect, in addition to the configuration of the fourth aspect, the measuring means for measuring the distance between each of the recording layers at a plurality of positions in the multilayer optical disc, and the measuring means for measuring the distance. Storage means for storing the distance together with the position, and a determination means for determining the predetermined voltage based on the distance and the position stored in the storage means.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

FIG. 1 is a block diagram showing an overall configuration of an optical disk reproducing apparatus according to an embodiment of the present invention. Referring to FIG. 1, a two-layer optical disc 1 having two recording layers
An optical disc reproducing apparatus 12 for reproducing 0 is a spindle motor 11 for rotating the two-layer optical disc 10 and an optical pickup device (PU) 14 for irradiating the two-layer optical disc 10 with a laser beam and reading information recorded on a recording layer.
And a reproduction signal RF, a force error signal FE, and a tracking error signal T from the optical pickup device 14.
A head amplifier 16 for amplifying E, an A / D converter 18 for AD-converting an output signal from the head amplifier 16,
A digital signal processor (DSP) 20 for processing an output signal from the D conversion unit 18 according to a predetermined program
A read-only memory (ROM) 22 in which a program for operating the DSP 20 is stored;
A random access memory (RAM) 24 for storing tables and the like created and used at 20;
D / A converter 26 for DA-converting the output signal from P20
And a driver 28 that drives an actuator 140 in the optical pickup device 14 in response to an output signal from the D / A converter 26.

FIG. 2 is a block diagram showing the configuration of the optical pickup device 14 shown in FIG. Referring to FIG. 2, optical pickup device 14 includes a semiconductor laser 141 that generates a laser beam, a half mirror 142 that reflects a laser beam from semiconductor laser 141 at right angles,
A multifocal collimator lens 143 that makes the laser beam from the half mirror 142 parallel or almost parallel, and a rising mirror 1 that reflects the laser beam from the multifocal collimator lens 143 in the Z (optical axis of the objective lens 145) direction.
44 and a laser beam from a rising mirror 144 provided opposite the two-layer optical disc 10 to the first recording layer 101.
Alternatively, the objective lens 14 that focuses on the second recording layer 102
5, an actuator 140 that performs focusing servo control by moving the objective lens 145 in the Z (optical axis) direction and performs tracking servo control by moving the objective lens 145 in the X (tracking) direction. A photodetector 146 that detects the laser beam reflected and transmitted through the collimator lens 143 and the half mirror 142, and a reproduction signal RF, a focus error signal FE, and a tracking error based on the detection signals DE1 to DE4 from the photodetector 146. A reproduction / FE / TE signal generation circuit 147 for generating the signal TE and a liquid crystal drive circuit 148 for driving the TN type liquid crystal 305 in the multifocal collimator lens 143 are provided.

Here, the half mirror 142, the multifocal collimator lens 143, the rising mirror 144, and the objective lens 145 constitute an optical system for guiding the laser beam from the semiconductor laser 141 to the double-layer optical disk 10.

As shown in FIG. 3, the multifocal collimator lens 143 includes a lens piece 301, a lens piece 302 facing the lens piece 301, a transparent electrode 303 formed on the inner surface of the lens piece 301, A transparent electrode 304 formed on the inner surface of the lens piece 302;
3 and 304, and a TN type liquid crystal 305 interposed therebetween. ITO, S as the transparent electrodes 303 and 304
nO ₂ , TiO _{2 and the} like are preferably used. Also, T
STN type liquid crystal or the like may be used instead of the N type liquid crystal 305.

The liquid crystal drive circuit 148 applies a predetermined voltage between the transparent electrodes 303 and 304 of the multifocal collimator lens 143 in response to an output signal from the driver 28 shown in FIG.

FIG. 4 is a graph showing the relationship between the refractive index of the TN type liquid crystal 305 and the applied voltage, and FIG. 5 is an enlarged graph of a main part in FIG. As shown in FIGS. 4 and 5, the refractive index of the TN type liquid crystal 305 changes according to the voltage applied between the transparent electrodes 303 and 304. Therefore, the focal length of the multifocal collimator lens 143 changes according to the applied voltage. The distance from the substrate surface of the dual-layer optical disc 10 to the focal point of the laser beam and the TN type liquid crystal 30
FIG. 6 shows the relationship with the refractive index of No. 5.

The photodetector 146 is composed of four split sensors 601 to 604 as shown in FIG. The split sensors 601 to 604 generate detection signals DE1 to DE4 according to the amounts of light received by the laser beams, respectively.

The reproduction / FE / TE signal generation circuit 147
The sum of the detection signals DE1 to DE4 is converted to a reproduction signal RF (= DE
1 + DE2 + DE3 + DE4), and outputs the sum of the detection signals DE1 and DE3 and the detection signal DE2.
And the difference from the sum of DE4 and the focus error signal FE
Output as (= (DE1 + DE3)-(DE2 + DE4)).

The actuator 140 is, as shown in FIG. 8, a lens holder 70 for holding the objective lens 145.
1, a focus coil 702 wound around the lens holder 701, tracking coils 703a and 703b attached to both ends of the focus coil 702 in the Y direction, and attached to both ends of the lens holder 701 in the X direction. Four leaf springs 704, a fixing base 705 supporting the leaf springs 704, yokes 707 inserted into two concave portions 706 of the lens holder 701, a focus coil 702, a tracking coil 703 a,
Permanent magnet 708 for applying a magnetic field perpendicular to 703b
And a yoke 709 supporting the permanent magnet 708 and a yoke base 710 supporting the yokes 707 and 709.

The driver 28 shown in FIG. 1 generates a focus drive voltage in response to a focus error signal, and the generated focus drive voltage is applied to the focus coil 7.
02 is applied. Thereby, the lens holder 701 moves in the Z (optical axis) direction so that the laser beam is focused on the first recording layer 101 or the second recording layer 102 of the two-layer optical disc 10. The driver 28 further generates a tracking drive voltage in response to the tracking error signal TE, and the generated tracking drive voltage is applied to the tracking coils 703a and 703b. Accordingly, the lens holder 701 is set to X (tracking) so that the laser beam is always irradiated on the track of the optical disc 10.
Move in the direction.

The ROM 22 stores programs as shown in FIGS. 9 shows a routine for measuring the distance between the first recording layer 101 and the second recording layer 102 at a plurality of positions in the dual-layer optical disc 10. The flowchart of FIG.
The transparent electrodes 303 and 304 are referred to with reference to a table of measurement positions and interlayer distances (Table 2 described later) stored in M24.
Shows a routine for determining a voltage to be applied during the period.

The ROM 22 also stores a table as shown in Table 1 below. This table is 2
Signal recording surface (recording layer) from substrate surface of layered optical disk 10
The relationship between the distance to the TN type liquid crystal 305 and the voltage applied to the TN liquid crystal 305 is shown.

[0029]

[Table 1]

Next, the operation of the optical disk reproducing apparatus shown in FIGS. 1 and 2 will be described. First, the operation of measuring the interlayer distance will be described with reference to the flowchart shown in FIG.

When the optical disk is mounted on the spindle motor 11, it is determined whether or not the mounted optical disk is a double-layer DVD (S1). If it is a two-layer DVD, the process proceeds to step S3. If it is not a two-layer DVD, the process proceeds to another step.

Subsequently, the optical pickup device 14 moves in the radial direction of the two-layer optical disc 10 and stops at the inner periphery (track number "40245") of the two-layer optical disc 10 as shown in FIG. S3). Then, the focus search is started at that position (S4). More specifically, the driver 28 increases or decreases the focus drive voltage applied to the focus coil 702 according to an instruction from the DSP 20. As a result, the objective lens 145 moves in the direction of the optical axis, and the reproduction / FE / TE signal generation circuit 147 outputs a focus error signal FE as shown in FIG. Since the two-layer optical disc 10 has two recording layers 101 and 102, two S-shaped curves appear in the focus error signal FE. DSP20
Are two peaks P3 and P4 of such an S-shaped curve.
, The distance between the first recording layer 101 and the second recording layer 102 at the track number “40245” is calculated (S5), and the distance is calculated as the track number “40”.
245 "and the RAM 24 (S6). Thus, the focus search on the inner circumference of the disc is completed (S7).

Subsequently, the optical pickup device 14 moves to the position of the track number "82134" (S8), and the DSP 20 performs a focus search as in the above steps S4 to S7 (S9). As a result, the track number “82”
134 is stored in the RAM 24 together with the track number.

Similarly, the optical pickup device 14 moves in the radial direction, the DSP 20 calculates the interlayer distance at a plurality of positions in the double-layer optical disk 10, and stores the calculated distance in the RAM 24 together with the track number indicating the position. It is stored (S10 to S13).

FIG. 11A further shows the optical pickup device 14 stopped at the center of the disk to measure the interlayer distance at the center of the disk, and stopped at the center of the disk to measure the interlayer distance at the periphery of the disk. The optical pickup device 14 is shown. FIG.
(C) shows the focus error signal FE output from the reproduction / FE / TE signal generation circuit 147 when the focus search is performed at the center of the disk. FIG. 11D shows the reproduction / FE / TE signal generation circuit 1 when a focus search is performed on the outer periphery of the disk.
The focus error signal FE output from 47 is shown.

As a result, a table as shown in the following Table 2 is stored in the RAM 24.

[0037]

[Table 2]

Next, a reproducing operation by the optical disk reproducing apparatus 10 will be described with reference to FIG.

First, when reproducing information from the first recording layer 101, the transparent electrode 303 of the multifocal collimator lens 143 is reproduced.
No voltage is applied between (A) and (304V). As shown in FIG. 5, when no voltage is applied, the refractive index of the TN type liquid crystal 305 is 1.500. Thus, as shown in FIGS. 2 and 12,
The laser beam emitted from the semiconductor laser 141 and reflected by the half mirror 142 is a multifocal collimator lens 143.
Parallelized by Multifocal collimator lens 143
Are reflected by the rising mirror 144 and then enter the objective lens 145. This parallel laser beam is applied to the first recording layer 10 by the objective lens 145.
Focused on 1.

The laser beam reflected by the first recording layer 101 returns to the half mirror 142 via the objective lens 145, the rising mirror 144, and the multifocal collimator lens 143, passes through the half mirror 142, and passes through the photodetector. 1
It is incident on 46. Then, the reproduction / FE / TE signal generation circuit 147 detects the detection signals DE1 to D from the photodetector 146.
E4, the reproduction signal RF and the focus error signal F
E and a tracking error signal TE are generated.

Here, in order to immediately start reproducing the information of the second recording layer 102 while reproducing the information of the first recording layer 101, the focal point of the laser beam by the objective lens 145 is set to the first focal point. Recording layer 101 to second recording layer 10
Need to move to 2. In order to perform such a focus jump, the DSP 20 determines an appropriate applied voltage to the TN type liquid crystal 305 according to the flowchart of FIG.

More specifically, the DSP 20 reads the currently reproduced track number from the first recording layer 101 (S2).
1) Referring to the table of Table 2 stored in the RAM 24, the interlayer distance at the track number is read (S2).
2). Subsequently, the DSP 20 calculates the distance from the substrate surface of the two-layer optical disc 10 to the signal recording surface of the second recording layer 102 based on the read interlayer distance, and further refers to the table of Table 1 to obtain a TN type liquid crystal. The voltage applied to 305 is read (S23). As a result, the optimum applied voltage for performing the focus jump on the currently reproduced track is determined.

If the currently reproduced track number is not listed in Table 2, the DSP 20 reads the inter-layer distance between the track numbers before and after that, and calculates the inter-layer distance at the currently reproduced track number by interpolation. Similarly, when the distance from the substrate surface to the signal recording surface is not shown in Table 1, the DSP 20 reads the applied voltage corresponding to the distance before and after the distance, and calculates the applied voltage corresponding to the calculated distance by interpolation. I do.

After determining the applied voltage, the DSP 20 sends the signal to the liquid crystal drive circuit 14 via the D / A converter 26 and the driver 28.
8 to the transparent electrodes 303 and 30.
4 is applied. Thereby, the liquid crystal drive circuit 148 applies the determined voltage between the transparent electrodes 303 and 304. For example, when a voltage of 4.0 V is applied, the refractive index of the TN type liquid crystal 305 changes from 1.500 to 1.510 as shown in FIGS. Thereby, the focal length of the multifocal collimator lens 143 becomes longer.

Therefore, as shown in FIGS. 2 and 13, the half mirror 1
The laser beam reflected at 42 is slightly wider than parallel by the multifocal collimator lens 143. Then, the laser beam is reflected by the rising mirror 144, then enters the objective lens 145, and is focused on the second recording layer 102 by the objective lens 145.

The laser beam reflected by the second recording layer 102 is incident on the photodetector 146 in the same manner as in the case of the first recording layer 101 described above, whereby the reproduction signal RF, the focus error signal FE, and the tracking error Signal TE
Is generated.

As described above, the optical disk reproducing apparatus 1
According to 2, the focal length of the multifocal collimator lens is changed by changing the refractive index of the TN type liquid crystal 305 inserted in the multifocal collimator lens 143, and thereby the focal point of the laser beam by the objective lens 145 is changed. Since the objective lens 145 is moved, the focus jump can be performed more quickly than in a conventional mechanical method of moving the objective lens 145 in the Z (optical axis) direction, and a failure hardly occurs.

The interlayer distance is measured in advance at a plurality of positions in the two-layer optical disk 10 and the distance is stored together with the position. Based on the stored distance and position, the optimum voltage applied to the TN type liquid crystal 305 is determined. Is determined, the focus jump can be accurately performed even with a two-layer optical disc having a variation in interlayer distance.

Although the embodiments of the present invention have been described in detail, the scope of the present invention is not limited by the above embodiments.

For example, a liquid crystal may be inserted in the objective lens instead of the collimator lens. Also, the transparent electrode 30
A transparent member having a controllable refractive index may be inserted into the lens in place of 3, 304 and the TN type liquid crystal 305,
In short, any configuration is possible as long as the focal length of the lens can be changed according to the recording layer to be reproduced.

In the above embodiment, the focus search is performed by moving the objective lens 145 in the Z (optical axis) direction by the actuator 140. However, the voltage applied to the TN type liquid crystal 305 in the multifocal collimator lens 143 The present invention may be variously modified, modified, and modified based on the knowledge of those skilled in the art without departing from the spirit of the present invention, such as by performing a focus search by continuously changing.
The present invention can be implemented in a modified form.

[0052]

According to the optical disk reproducing apparatus of the present invention, since the focal length of the lens is changed according to the recording layer to be reproduced, the focus jump can be quickly performed.

Further, since the liquid crystal is inserted into the collimator lens and a predetermined voltage is applied between the transparent electrodes on both sides of the liquid crystal according to the recording layer to be reproduced, the focus jump can be performed more quickly than the conventional mechanical method. It can be performed, and is less likely to fail.

Further, the interlayer distance is measured at a plurality of positions in the multilayer optical disk, the distance is stored together with the position, and a predetermined voltage to be applied between the transparent electrodes on both sides of the liquid crystal based on the stored distance and position. Is determined, the focus jump can be accurately performed even for a multilayer optical disc having a variation in interlayer distance.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of an optical disc reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of the optical pickup device shown in FIG.

FIG. 3 is a side view showing a configuration of the multifocal collimator lens shown in FIG.

FIG. 4 is a graph showing a relationship between a refractive index of the TN type liquid crystal shown in FIG. 3 and an applied voltage.

FIG. 5 is an enlarged graph of a main part of the graph shown in FIG. 4;

FIG. 6 shows the optical pickup device shown in FIG.
Fig. 3 shows the distance from the substrate surface of the multilayer optical disc to the focal point
6 is a graph showing a relationship between the TN type liquid crystal and the refractive index shown in FIG.

FIG. 7 is a plan view showing a configuration of the photodetector shown in FIG.

FIG. 8 is a perspective view showing the structure of the actuator shown in FIGS. 1 and 2.

9 is a flowchart showing an operation of measuring an interlayer distance stored in the ROM shown in FIG.

FIG. 10 is a flowchart showing an operation of determining an applied voltage stored in a ROM shown in FIG. 1;

11A is an explanatory diagram showing an operation of measuring an interlayer distance shown in FIG. 9, and FIG. 11B is a waveform diagram showing a focus error signal obtained when a focus search is performed on the inner circumference of the disk. (C) is a waveform diagram showing a focus error signal obtained when a focus search is performed on the center of the disk, and (d) is a waveform diagram showing a focus error signal obtained when a focus search is performed on the periphery of the disk. It is a waveform diagram shown.

FIG. 12 is an explanatory diagram showing an optical path of a laser beam when a voltage is not applied to a transparent electrode in the multifocal collimator lens shown in FIG. 3;

13 is an explanatory diagram showing an optical path of a laser beam when a voltage is applied to a transparent electrode in the multifocal collimator lens shown in FIG.

[Explanation of symbols]

 Reference Signs List 10 double-layer optical disk 12 optical disk reproducing device 14 optical pickup device 20 digital signal processor (DSP) 22 read only memory (ROM) 24 random access memory (RAM) 141 semiconductor laser 143 multifocal collimator lens 145 objective lens 148 liquid crystal drive circuit 301, 302 Lens piece 303, 304 Transparent electrode 305 TN type liquid crystal

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroshi Watanabe 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor 2-5-5 Sanyo Electric Co., Ltd. (72) Inventor Shuichi Ichiura 2-5-5 Keihanhondori, Moriguchi-shi, Osaka F-term in Sanyo Electric Co., Ltd. 5D118 AA00 AA11 BA01 BB01 BB08 BF16 CA11 CD06 DC03 DC05 5D119 AA28 BB11 BB13 DA12 EA03 JA02 JA54 JB01 JB03

Claims (5)

[Claims] 1. An optical disc reproducing apparatus for reproducing a multi-layer optical disc having a plurality of recording layers, comprising: a laser; an optical system including a lens for guiding a laser beam from the laser to the multi-layer optical disc; An optical disc reproducing apparatus, comprising: changing means for changing a focal length of the lens according to a recording layer to be reproduced among the recording layers. 2. The method according to claim 1, wherein the lens is a collimator lens.
The optical disk reproducing device according to claim 1. 3. A collimator lens comprising: a first lens piece; a second lens piece provided to face the first lens piece; and a first lens piece sandwiched between the first and second lens pieces. 3. The optical disc reproducing apparatus according to claim 2, wherein the changing unit changes a refractive index of the transparent member according to a recording layer to be reproduced among the plurality of recording layers. 4. The transparent member includes: a first transparent electrode; a second transparent electrode provided to face the first transparent electrode; and a first transparent electrode sandwiched between the first and second transparent electrodes. The changing means includes a liquid crystal drive circuit that applies a predetermined voltage between the first and second transparent electrodes according to a recording layer to be reproduced among the plurality of recording layers. An optical disc reproducing apparatus according to claim 3. 5. A measuring means for measuring a distance between each of the recording layers at a plurality of positions in the multilayer optical disc; a storing means for storing the distance measured by the measuring means together with the position; The optical disk reproducing apparatus according to claim 4, further comprising: a determination unit that determines the predetermined voltage based on the distance and the position stored in the unit.